Heat exchanger and associated method

ABSTRACT

A heat exchanger for cooling a machine fluid of a vehicle, and associated method. The heat exchanger can include a fluid inlet tank, a fluid outlet tank, and a plurality of heat transfer tubes connecting the inlet tank to the outlet tank. Each tube can include first and second substantially flat sidewalls, a plurality of internal webs extending between the first and second sidewalls, and a plurality of first dimples formed on the first sidewall, each first dimple formed over one of the webs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/404,015 filed on Mar. 31, 2004 which claims the benefit ofU.S. Provisional Application No. 60/375,920 filed on Apr. 25, 2002. Thedisclosures of these applications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to the area of cooling of the fluids thatare used in machinery such as engines, transmissions and other powerequipment to lubricate components and/or transfer power.

INTRODUCTION

In the automotive industry it is necessary to cool the oil used inautomatic transmissions. The automotive transmission fluid (ATF) reacheshigh temperatures in the operation of the transmission. These hightemperatures need to be reduced to avoid breakdown of the fluid. Adevice called a transmission oil cooler is conventionally used for thatpurpose.

With reference to the simplified prior art view of FIG. 1, a typicaltransmission cooler 3 is illustrated in an automotive application. Theexemplary application is shown to generally include an engine 4 and atransmission 5. The oil cooler 3 is typically located inside one of thetanks 2 of a radiator 1. The coolant inside the tanks 2 is used as thecooling medium for the oil cooler 3. This is possible despite the factthat the coolant itself is relatively hot, because the oil temperatureis substantially higher. The temperature differential between thecoolant in the radiator tank 2 and the oil in the oil cooler 3 is usedto cool the oil. The oil circulates through hydraulic lines 6 betweenthe transmission 5 and the oil cooler 3, and the oil gets cooled in theheat exchanger 3.

FIG. 2 illustrates one typical transmission oil cooler 3 in furtherdetail. The oil cooler 3 is located inside the tank 2 of radiator 1.This type of oil cooler, which consists of concentric brass tubesbetween which the oil flows, is typically made by brazing, a hightemperature process that requires expensive brazing equipment andcomplex process control. The result is a relatively expensive and heavyoil cooler. FIG. 2A shows the cross section of the oil cooler.

FIG. 3 shows a more modern transmission oil cooler 3′. The oil cooler 3′is again located inside the tank 2 of radiator 1. This type of oilcooler 3′ is called a plate cooler, because it basically consists ofseveral flat plates inside which the oil flows. Plate oil coolers aretypically made using aluminum strips which are joined together alongtheir perimeter in a brazing process. The use of flat plates leads to abetter heat exchange performance than for a concentric tube cooler, butthe result is still a relatively expensive and heavy oil cooler. Thevery large number and length of brazed joints creates many potentialfailure modes (leaks), which has a potential negative impact on thereliability of this oil cooler.

FIG. 4 shows an engine oil cooler 7 that can be used in addition to thepreviously shown transmission oil cooler 3. Some vehicles require bothoil coolers. Virtually every vehicle with an automatic transmissionrequires a transmission oil cooler, and many high powered or high rpmengines require also an engine oil cooler. Typically the engine coolerand the transmission oil cooler are on two separate, independent coolingcircuits. The engine oil circulating through the engine oil cooler 7 istypically cooled by placing the oil cooler 7 in a housing that containscoolant. Another possibility (not shown here) is to place the engine oilcooler in the second radiator tank (the first one is already occupied bythe transmission oil cooler).

While known oil coolers have proven to be suitable for their intendedpurposes, a need remains in the pertinent art for a lightweight, lowcost, highly reliable oil cooler and other heat exchanger with highlyefficient heat transfer characteristics.

SUMMARY

The present teachings provide a heat exchanger for cooling a machinefluid of a vehicle. The heat exchanger can include a fluid inlet tank, afluid outlet tank, and a plurality of heat transfer tubes connecting theinlet tank to the outlet tank. Each tube can include first and secondsubstantially flat sidewalls, a plurality of internal webs extendingbetween the first and second sidewalls, and a plurality of first dimplesformed on the first sidewall. Each first dimple can be formed over oneof the webs.

The present teachings also provide a method for making a heat exchangerfor cooling a machine fluid. The method includes forming a plurality oftubes having first and second substantially flat sidewalls, coupling afirst end of each tube to a fluid inlet tank, coupling a second end ofeach tube to a fluid outlet tank, forming webs between the first andsecond sidewalls of each tube, and forming a plurality of first dimpleson the first sidewall of each tube, each first dimple formed over one ofthe webs.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the embodiment of the invention, are intended for purposes ofillustration only and are not intended to limit the scope of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a prior art transmission heatexchanger circuit;

FIG. 2 is a view of a prior art conventional heat exchanger ofconcentric tube design shown in partial section;

FIG. 2A is a cross-sectional view taken along the line 2A-2A;

FIG. 3 is a view of another prior art heat exchanger of plate designshown in partial section;

FIG. 4 is a schematic illustration of prior art engine heat exchangerand transmission heat exchanger circuits;

FIG. 5 is a top view of a heat exchanger according to the presentteachings;

FIG. 6 is a side view of the heat exchanger of FIG. 5;

FIG. 6A is a cross-sectional view taken along the line 6A-6A;

FIG. 7 is a top view of a heat exchanger according to the presentteachings;

FIG. 8 is a top view of a heat exchanger according to the presentteachings;

FIG. 9 is a top view of a heat exchanger according to the presentteachings;

FIG. 10A is a cross-sectional view of a heat transfer tube of a heatexchanger according to the present teachings;

FIG. 10B is a cross-sectional view of the tube of FIG. 10A taken along aline perpendicular to the line of the FIG. 10A cross-section;

FIG. 11A is a cross-sectional view of a tube of a heat exchangeraccording to the present teachings;

FIG. 11B is a cross-sectional view of the tube of FIG. 11A taken alongthe line perpendicular to the line of the FIG. 11A cross-section;

FIG. 12A is a cross-sectional view of a tube of a heat exchangeraccording to the present teachings;

FIG. 12B is a cross-sectional view of the tube of FIG. 12A taken alongthe line perpendicular to the line of the FIG. 12A cross-section;

FIG. 13 is a side view of a portion of a tube of a heat exchangeraccording to the present teachings;

FIG. 13A is a cross-sectional view taken along the line 13A-13A;

FIG. 14 is a top view of a heat exchanger according to the presentteachings;

FIG. 15 is a side view of the heat exchanger of FIG. 14;

FIG. 16 is a top view of a heat exchanger according to the presentteachings;

FIG. 17 is a side view of the heat exchanger of FIG. 16;

FIG. 18 is a top view of an air-cooled heat exchanger in accordance withthe teachings of the present invention;

FIG. 19 is a side view of the heat exchanger of FIG. 18;

FIG. 20 is a side view of a heat exchanger according to the presentteachings;

FIG. 21 is a top view of the heat exchanger of FIG. 20;

FIG. 22 is a cross-sectional view taken along the line 22-22 of FIG. 20;and

FIG. 23 is a cross-sectional view taken along the line 23-23 of FIG. 20.

DETAILED DESCRIPTION

The following description of various aspects of the invention is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. The present teachings are applicable, but arenot limited to, the area of cooling of transmission oil and/or engineoil in automotive applications. The present teachings are, for example,also applicable to diverse areas such as railways, ships, aircraft,machine tool, power generation equipment and others.

Referring to FIG. 5, an exemplary heat exchanger, such as for example,an oil cooler, is illustrated and identified at reference character 10according to an aspect of the present teachings. The heat exchanger 10is shown to generally include first and second end tanks 12 and 14. Theend tanks 12 and 14 can be round or circular in shape. The end tanks 12and 14 can be connected by a plurality of heat transfer tubes 16. In theexemplary illustration of FIG. 5, the heat exchanger 10 is shown toinclude five such tubes 16, although any number of tubes 16 can be used.The tubes 16 may be brazed to the end tanks 12 and 14. The first endtank 12 defines a first port 18 as the inlet of oil to be cooled and thesecond end tank 14 defines a second port 20 as the outlet. Typically,the ends of the tanks 12, 14 can threaded or equipped with some type ofconnector that allows the connection to the hydraulic lines leading theoil. The complete heat exchanger 10 can be immersed in a cooling medium,such as radiator coolant, typically a mixture of 50% water and 50%glycol. The heat of the oil is transferred through the tube walls to thecooling medium, so that the temperature of the oil leaving the heatexchanger 10 is significantly lower than the temperature of the oilflowing into the heat exchanger 10.

FIG. 7 illustrates another exemplary heat exchanger 30 that includesthree tubes 16 adapted for applications, for example, in which less heattransfer is required. FIG. 8 illustrates another exemplary heatexchanger 32 in which four tubes 16 are used. FIG. 9 illustrates anotherexemplary heat exchanger 34 with six tubes 16, for applications in whichgreater heat transfer is desirable.

Referring to FIG. 10A, an enlarged cross-section of one of the tubes 16is illustrated. In the exemplary aspect of FIG. 10A, the tube 16 isshown to include a pair of sidewalls 38, and internal webs 40 connectingthe sidewalls 38. The internal webs 40 are incorporated to providestrength to the tube 16 to meet the requirement of a high-pressure testthat the heat exchanger 10 must pass for validation. FIG. 10B is across-sectional view of tube 16 of FIG. 10A taken along a lineperpendicular to the cross-sectional line of FIG. 10A.

FIGS. 11A and 11B illustrate another exemplary aspect of the tubes 16according to the present teachings. In this aspect, the tube 16 caninclude indentations 44 along the full width of the tube 16, alternatelyspaced on both sidewalls 38 of the tube 16. Turbulation of the flowthrough the tubes 16 occurs at each indentation 44, increasing the heattransfer.

Referring to FIGS. 12A and 12B, an exemplary tube 16 can include dimples46 that are formed alternately on both sidewalls 38 of the tube 16 andlocated between the internal webs 40. The dimples 16 can be of round,circular, oval or other shapes as desired. Turbulation of the flowthrough the tubes 16 occurs at each dimple 46, increasing the heattransfer.

Referring to FIGS. 13 and FIGS. 13A, exemplary tubes 16 can includedimples 46 formed on one of the sidewalls 38 in a staggered or zigzagpattern. In the exemplary illustration of FIGS. 13 and 13A, the oppositesidewall 38 does not include any dimples 46.

Referring to FIGS. 14 and 15, an exemplary heat exchanger 50 accordingto the present teachings can include a plurality of tubes 16, with eachtube defining a convoluted shape having convolutions 51. The multipledirection change of each tube 16 provides good turbulence for efficientheat transfer. The heat exchanger 50 can also include round, rectangularor otherwise shaped end tanks 12 and 14. Each tube 16 can also includeturbulators 49, which are inserted within the passages of the tube 16,for providing additional turbulence. These turbulators 49 can be piecesof bent wire or bent metal strips, etc.

With reference to FIGS. 16 and 17, another exemplary heat exchanger 52having convoluted tubes 16 can include first and second end tanks 54 and56 that are rectangular in shape. Other shapes of end tanks 54, 56 canbe used, such as oval, elliptical or of other polygonal or curved, asdesired in a particular application.

Referring to FIGS. 18 and 19, an exemplary heat exchanger 60 that isair-cooled is illustrated. In contrast to the previously described heatexchangers 10, 30, 32, 50, 52, the heat exchanger 60 is not immersed ina cooling liquid, but instead it releases its heat to the surroundingair, similar to a typical engine radiator. The heat exchanger 60 caninclude fins 62 placed between tubes 16 to provide additional coolingsurface. The heat exchanger 60 can include end tanks 54 and 56 that canbe circular, round, rectangular, oval or any other shape desired.

Referring to FIGS. 20-23, another aspect of a heat exchanger constructedin accordance with the present teachings is illustrated and generallyidentified at reference character 100. For automotive applications, theheat exchanger 100 can be mounted within one of the tanks of theradiator that is used to cool the engine of the vehicle. The heatexchanger 100 can be, for example, an automotive transmission oilcooler, or other type of cooler. The heat exchanger 100 can generallyinclude first and second end tanks 12 and 14. The end tanks 12 and 14can be connected by a plurality of heat transfer tubes 102. The tubescan be extruded from aluminum or otherwise made from differentmaterials. In some applications, the tubes 102 can be rigid and/orsubstantially flat. The tubes 102 can be brazed or otherwise suitablyattached to the tanks 12 and 14 in a manner well-known in the art. Asdescribed above, the heat of the oil can be transferred through the tubewalls to the cooling medium, so that the temperature of the oil leavingthe heat exchanger 100 is significantly lower than the temperature ofthe oil flowing into the heat exchanger 100. Dimples or indents 104 canbe formed on each sidewall of each heat transfer tube 102 to improveheat exchange.

The required cooling efficiency of a transmission oil cooler isgenerally higher than the efficiency required for other automotivecooling devices, such as radiators. For such applications, the dimples104 of the heat exchanger 100 can be configured to improve the thermalcapacity of the tubes 102 to meet applicable requirements. According tothe present teachings, the dimples 104 can deep enough to provideadequate turbulation without tearing or fracturing the sidewalls of thetubes 102. The associated dimpling process is adapted to be repeatableand consistent and avoids variability in the cooling performance of theheat exchangers 100. The dimples 104 are configured such that they donot affect the ability of the heat exchanger 100 to withstand pressuresof the order of 500 psi.

Referring to FIGS. 20, 22 and 23, an exemplary arrangement of dimples104 according to the present teachings is illustrated. A plurality offirst dimples 104 a formed on a first sidewall 38 a of the tube 102 isillustrated in solid lines. A plurality of second dimples 104 b formedon a second sidewall 38 b of the tube 102 is illustrated in phantomlines. The first and second dimples 104 a, 104 b are formed directlyover alternating webs 40 a, which are shortened to accommodate the depthof the dimples 104 a, 104 b. The dimples 104 a, 104 b can be formedcentrally relative to the respective webs 40 a, 40 b. The first dimples104 a on the first sidewall 38 a can be shifted relative to the seconddimples 104 b on the second sidewall 38 b by one web, such that the webs40 a corresponding the first dimples 104 a alternate with the webs 40 bthat support the second dimples 104 b. In particular, each first dimple104 a is centered over a first web 40 a and extends to two adjacentsecond webs 40 b on each side of the first web 40 a. Similarly, eachsecond dimple 104 b is centered over a second web 40 b and extends totwo adjacent first webs 40 a on each side of the second web 40 b.Forming the first and second dimples 104 a, 104 b directly over one ofthe first and second webs 40 a, 40 b allows the formation of much largerdimples that can extend nearly to the adjacent web on either side of theweb central to the dimple without any tearing of sidewall metal. Thedimples 104 a, 104 b can be formed very consistently because the webs 40a, 40 b provide metal restraint on the punch used for the forming. Thedimples 104 a, 104 b can be round, circular, oval, rectangular or haveay other shape.

Referring to FIG. 22, two fluid flow passages 117 bounded by first andsecond webs 40 a, 40 b are formed between each of the first dimples 104a and the second sidewall 38 b. Referring to FIG. 23, two fluid flowpassages 117 bounded by first and second webs 40 a, 40 b are also formedbetween the second dimples 104 b and the first sidewall 38 a. Each fluidflow passages 117 can have a substantially triangular shape, with oneside following the curve defined by the corresponding dimple 104 a, 104b. The second dimples 104 b can be offset transversely by one web 40 bfrom the webs 40 a that are central to first dimples 104 a. Thearrangement of the first and second dimples 104 a, 104 b defines acontinuing and very frequent change in fluid flow passage position andarea, and creates enough turbulence to meets the critical criteria fortransmission oil coolers.

In one aspect, the cross-sectional dimensions of the heat transfer tubes102 can be, for example, about 2.8 mm by 34 mm, and the spacing betweenadjacent webs 40 can be about 2.5 mm.

It will be appreciated from the above description that the presentteachings provide a lightweight, low cost, highly reliable heatexchanger with highly efficient heat transfer characteristics. Further,the heat exchanger can increase reliability and reduces/eliminatespotential failure modes, such as leaks. Extruded aluminum tubes can beused as part of the heat transfer mechanism. Extruded tubes simplify themanufacturing process, and reduce or eliminate potential failure modes(leaks), which directly impact reliability, production cost, testingcost and warranty costs. The use of extruded tubes dramatically reducesthe need to join surfaces through brazing in a watertight and oil tightmanner. Since every joint in a pressurized heat exchanger is always apotential failure mode, the elimination or reduction in the number ofjoints provides a major reliability advantage.

Further increase in the heat transfer capability of the heat exchangercan be provided by modifying the extruded tubes, for instance, bybending or convoluting them or creating dimples in them in order toincrease turbulence in the tubes. Further increase the heat transfercapability of the heat exchanger can be provided by modifying thecross-section of the extruded tubes in ways that increase heat exchange.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A heat exchanger for cooling a machine fluid of a vehicle, the heatexchanger comprising: a fluid inlet tank; a fluid outlet tank; and aplurality of heat transfer tubes connecting the inlet tank to the outlettank, wherein each tube comprises: first and second substantially flatsidewalls; a plurality of internal webs extending between the first andsecond sidewalls; and a plurality of first dimples formed on the firstsidewall, each first dimple formed over one of the webs.
 2. The heatexchanger of claim 1, wherein the first dimples are formed overalternate webs of the tube.
 3. The heat exchanger of claim 2, furthercomprising a plurality of second dimples formed on the second sidewallof each tube, each second dimple formed over one of the webs.
 4. Theheat exchanger of claim 3, wherein the second dimples are offsetlaterally by one web relative to the first dimples.
 5. The heatexchanger of claim 1, wherein each first dimple is formed substantiallycentrally relative to the corresponding web.
 6. The heat exchanger ofclaim 4, wherein each of first and second dimples are formedsubstantially centrally relative to the corresponding webs.
 7. The heatexchanger of claim 1, wherein each first dimple defines a pair of fluidflow passages between the first dimple and the second sidewall.
 8. Theheat exchanger of claim 3, wherein each second dimple defines a pair offluid flow passages between the second dimple and the first sidewall. 9.The heat exchanger of claim 6, wherein the dimples have shapes selectedfrom the group consisting of oval, square, rectangular, polygonal,circular and rounded.
 10. The heat exchanger of claim 1, adapted forimmersion in a cooling liquid.
 11. The heat exchanger of claim 1,adapted for air-cooling.
 12. The heat exchanger of claim 1, wherein thetubes are connected to the inlet and outlet tanks by brazing.
 13. Theheat exchanger of claim 1, wherein the tubes are extruded from aluminum.14. The heat exchanger of claim 1, further comprising cooling finspositioned between the tubes.
 15. The heat exchanger of claim 1, whereinthe machine fluid comprises transmission fluid.
 16. A method for makinga heat exchanger for cooling a machine fluid, the method comprising:forming a plurality of tubes having first and second substantially flatsidewalls; coupling a first end of each tube to a fluid inlet tank;coupling a second end of each tube to a fluid outlet tank; forming websbetween the first and second sidewalls of each tube; and forming aplurality of first dimples on the first sidewall of each tube, eachfirst dimple formed over one of the webs.
 17. The method of claim 16,further comprising forming the first dimples over alternate webs. 18.The method of claim 17, further comprising forming a plurality of seconddimples on the second sidewall of each tube over alternate webs of thetube.
 19. The method of claim 18, wherein forming the second dimplescomprises offsetting the second dimples laterally by one web relative tothe first dimples.
 20. The heat exchanger of claim 1, wherein the firstand second dimples are formed substantially centrally relative to thecorresponding webs.